Re: fc-2
what glock said, but you can use the triangle at the bottom for some compensation, from top to bottom, that triangle itself is 5moa, from the center dot to the top of the triangle is 10 moa and to the bottom is 15, so depending on your drop, you can work out a solution.
for instance, i shoot black hills reman 223 77 gr smk in my 16 inch ar, i zero at 100 yards, at 300 yards i used the bottom of the circle, at 400 i used the top of the triangle, it was a little low but you could hit an 8 inch target pretty easily, the bottom of the triangle is about 550, maybe 560 yards, but i didn't get to try it at that distance.